Method of and apparatus for comparing and recording relative intensity of radiant energy



Z50-201 AU 252 E FIPszlz xn 1,806,19); REFERENCE May 19, 1931. A C,HARDY ETAL 1,806,197 lETHoD OF AND APPARATUS FOR CONPARING AND RECORDINGRELATIVE INTENSITY 0F RADIANT ENERGY Filed June 1, 192'7 2 Sheets-Sheet1 5 0 g 0 1 CROSS REFERENCE .im n

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UNITED STATES APATENT OFFICE 'ARTHUR C. HARDY, 0l' WELLESLEY, SETTE, ANDmmm W. GU'NNING- HAI, '0l' STAIIORD, OONNECTICUT, ABBIGNOBB T0 GENERALmmc OOIPANY,

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.L CORPOBATIQN 0F NEW YORK moll) 0i' LND APABATUS FUR G'AND B-.GORDDGRELATIVE INTENBITY 0F BADIANT ENERGY i Application :Bled June 1, 1987.Burial lo. 195,848.

This invention pertains to a method of comparing or measur' radiantenergy (of which light, heat ande ectrical ener may be cited asexamples) and for recording the results of such comparison ormeasurement, and to apparatus useful in the practice of such method, andin its more limited aspects relates'to a method of and apparatus forcomparing or measuring and recording radiant ener of wave lengthsapproximating those o light. Merely for convenience in descriptionand-as an illustrative example ofv one application of the broadprinciple underlying our invention we shall hereafter refer moreparticularly to its use in colorimetr ,that is to say, the comparison ofcolor samp es with one another or with a standard of comparison andespecially to the spectrophotometric analysis of a given color sample todetermine the relative intensity, at any or all wave lengths, of theluminous radiations emanating from said sample, and for convenience indescription the apparatus hereinafter referred to will be termed acolorimeter. p

Various methods of color comparison have heretofore been devised, butwhile there have been many suggestions in the prior art of methods ofand devices for determining the specific color of a surface and ofstating that specific color in terms such as definitely to identify thecolor referred to so that the arts and industries may be informed of theexact color, we are aware of no system of the sort of sufficientconvenience, suilicient accuracy, and suicient freedom from therequirement for skilled operation of the estimator of the color' toreach the large field of utility waiting for some such system. Painters,whether industrial or artistic, confectioners, dyers, dressmakers,potters, enamelers, electroplaters, printers of wall paper, textilefabrics and colored illustra' tive or display books, pictures orposters; weavers and finishers o textile fabrics; the makers ofpigments, paints, dyes and stains, as well asrmany others practicingindustrial arts are dependent upon guesswork or ocular estimation of thecolor of materials, or of surfaces, in the absence of any accuratesystem 'other of nomenclature, means for accurate mensurationv of thechromatic a pearances, or stem of standards re ating to color adapte toserve as ,the basis of communication from one artisan to another, andupon which the color of a surface can be yaccurately described. This isa considerable handicap in each of these arts.

Among the various methods employed for color comparison may be mentionedsystems of color sample cards, the Maxwell color disk, andspectrophotometric measurements, but none o the'se prior methods fullymeets commercial requirements, since in many arts the colordetermination, to be of any real value must be made uicklv and often bypersons who are not o the highest discernment pr'technical ability.Furthermore, in all of the'systems heretofore known to us theidiosyncrasy of the individual observer must alwa s be reckoned with asan indeterminate actor in the results of the observation, it being wellrecognized that the retina of the human eye diii'ers with eachindividual in its response to any given wave length of light. Moreover,the human eye is subject to fatigue which renders its response to color`vibrations even more uncertain, particularly when the eye is obliged tomake a long series of comparisons, while the texture of the surface ofcolor cards or similar means of comparison likewise affects the accuracyof the results of "comparative observation. ther, the human eye'observes but a small fraction of a sample surface at once, and as it isvery seldom that a color sam le is of absolutely uniform texture and coor throughout itsarea the result of ocular observation may vary quitematerially from the integrated color value of the entire surface of thesample. Even at best, the color card system, as ordinarily employed, andin the hands of a skilled observer furnishes but little as'sistance to-the investigator desirin to know how to treat a given sample to ma e itmatch a selected standard. For example, in preparing dyestuii's fordyeing textile fabrics it is often a diicult matter to determine in whatrespect a dye sample fails to match a given standard, that is to say,whether it is Furcross REFERENCE be applied.

On the other hand, while the ectrophotometric method of determination 1squite accurate (aside from the variable physiological error of theobserver) it is very slow and laborious, since for accurate results itis often necessary to make several hundred individual' observationswhich must then be plotted to indicate the result, and this methodnecessitates the employment of a skilled observer trained in the use ofinstruments of precision.

We have now discovered a method of comparing or measuring radiant energy1n general and which we find particularly applicable to the comparisonof the luminous energy of the spectrum and which is not affected by thecolor idiosyncrasy, fatigue or other physiological factors of theindividual observer which is applicable to the comparison of refiected,transmitted or emitted light; which permits rapid comparison of a samplewith a standard for determination of color intensity at any or all wavelengths; which integrates the color of the entire exposed surface of thesample; which provides a record of the determinations; and

which may be practiced by persons relatively unskilled in technicalmatters; and we have devised apparatus of simple and accurate characteruseful in the practice of this method.

Briefly stated, our method of comparison or measurement comprises thefundamental principle of causing radiant energy from two sources to becompared, whether one of such sources is a standard or not (the energybeing directed by any suitable means such, for example, as reiiectors,lens systems, etc.) to fall upon an electrical device which is highlysensitive to radiant energy of the kind to be compared or measured andthrough which device there flows an electrical current which isdependent in magnitude on the amount of energy which falls upon suchdevice. In accordance with our method the energy from the two sources tobe compared is caused alternately to fall upon a single sensitiveelectrical device, the rate of alternation' being relatively rapid, forexample, of the order of twenty cycles per second and thus, if theenergy from the two sources to be compared is unequal, a pulsatingcurrent will be set up in the sensitive electrical device. This devicemay, for example, be a photoelectric cell, a bolometer, a radiomete or,in fact, any other device of the same general character in which currentow varies with the amount of radiant energy delivered to the device.

Hereinafter, for convenience in description and illustration, we shallrefer to this device as a photoelectric cell but do not intend to limitourselves to this particular instrument, although for our purpose wefind it eminently satisfactory.

In making the comparison between the energy from the two sources wecause the pulsating current in the photoelectric cell to make itspresence known, either through a suitable o serving instrument orpreferably by means of an electrically actuated device adapted tooperate mechanical partsusuall amplifying this pulsating current bysuitab e means, for example, thermionic tubes or the like, andpreferably rectifying the pulsatin current to permit its use forobservationa purposes or actuation of the desired mechanism. Havingdetermined the existence of this pulsating current, either by means ofan indicating instrument, as above noted, or mechanically, we proceed tovary the energy received from one of the sources until the energy from'both sources, as received at the photoelectric cell is substantiallyequal, which may be determined by the fact that under such conditionsthe pulsations in the current through the cell cease, and the currentbecomes constant. If, as above stated, we employ amplifying meansbetween the cell and the observing instrument or other mechanismresponsive to such ulsating current, the amplification ceases w en thecurrent becomes steady, and thus the indicating instrument or othermechanism normally acting in response to the pulsating current ceases tofunct1on,thereb making it apparent that the energy receive from eachsource is the same.

When our broad method, above described, is to be applied to colorimetrwe prefer to dis erse beams of light on their way from eac of therespective sources to the photoelectric cell so as to form extendedalternating spectra, and we expose the cell progressivel to the variousparts of the s ectral ban s, for instance, at certain definite raunhoferlines beginning, for example, at the red end of the spectrum andprogressing toward the violet end. At each point of exposure of thephotoelectric cell to the spectrum, comparison is made of theintensities of the luminous radiations arrivin from the respectivesources, and this oservation may be noted by reference to indicatinginstruments and recorded manually, such records afterward bei plotted toform a color comparison curve, ut plreferably such a curve 1s formedmechanica y and automaticall by suitable mechanism under the control othe pulsating current in the photoelectric cell.

For comparing samples of pigment or other o aque colored samples, it 1snecessary to emp oy reflected li ht and as a standard of comparison weiin that magnesium carbonate (MgCO.) furnishes a uniformly pure whitegiving a very true and pure speca metal network or Lacan? trum band.Preferably, we di ose the' source of light between the Vstandar ,for example a block of magnesium carbonate, and the sample to be compared, andby the employment of suitable condensing enses if necessary interposingcooling cells in t e light paths), we direct beamsl of li ht from thesource of light onto the stan ard and onto the sample respectively. Wethen direct beams of rellected light from the standard and sample onto asuitable device adapted alternately to cut off the light from eachsource imd to permit the li ht from each source intermittently to pass trough a narrow slit, and thence to a dispersing prism,`

diffraction grating, or other instrument for producin an extendedspectrum band. By alternatey cutting off the light from the standard andfrom the sample we produce a iiickering spectrum band which alternatelyrepresents the light from the standard and from the sample. We thenexpose the photoelectric cell or equivalent device to this band,preferably shielding the cell and providin for exam le a narrow slitwhich permits ight from but a small portion of the band to impinge uponthe cell at any instant. We then move the slit lengthwise of the bandand by the use of mirrors, by moving the cell or preferably by the useof a quartz rod or tube, cause the i ht from the slit always to fallupon the cel In dealing with reiected light from a sample and souree,asabove described, it is evident that the energy at the spectrum band,after dispersion of the reflected ray, may be exceedingly small and forthis reason the sensitively responsive instrument, for example, thehotoelectric cell, must be of such character t at it will respond withgreat rapidity and with the utmost sensitiveness to minute variations inluminous ener y falling thereon. It is also desirable t at thissensitive instrument, whatever its nat-ure, be responsive to light wavesof any length throughout the spectrum. It is quite possible, 1f desired,to obtain a photoelectric cell which responds substantially uniformly tolight of a wide ran e of wave lengths. For our purpose we fin that aphotoelectric cell is practical and gives results of suiicient accuracy.Due to the extreme sensitiveness of such a cell in which the currentflow may be lof the order of l0'1o amp. we find it necessary in somecases to protect this cell from stray electrical disturbances byenclosing it within closed we find that t e .quartz tube or rodconstitutes a very convenient instrument for admitting the light to thecell, since such rod may pass throughs very small opening in theenclosing screen or grid without impairing the efficiency of the latter.

Since the current value in this cell is extremely small, .it isobviously of little value rid, and when so en-` for directly indicatingconditions or directly controlling auxiliary apparatus and thus, as

above described, we prefer t'o amplify this current, preferabliyly usingseveral stages of amplification of t e general type employed in radiowork. Preferably, we interpose condensers in this amplifyin system andthe amplified current is carrie to a rectif ing device which is drivensynchronous y with the means for alternately cuttin off the light fromthe sample and standar This rectifying device converts the am liiedpulsating current into a flow in one irectin or' the other whichactuates a s uitable relay, for example, a direct current galvanometer,which in turn may actuate other relays controlling the current through areversible electric motor, such motor actuating a shutter, diaphragm orother device for regulating the amount of light delivered from theilluminant to the sample, the standard, or both. For making an automaticrecord of the comparisons, we prefer to provide a stylus which isactuated by the same motor which operates the shutter, and we alsoprovide a drum or other moving surface with which the stylus cooperates,the drum or moving surface being driven by a second motor at suitablespeed and, if desired, carrying a sheet of paper or other material uponwhich the record is to be made. The drum motor'also actuates mechanismfor shifting the slit from one end of the spectrum to the other, andthus we provide continuously acting'mechanism which automaticallyrecords the color intensity throughout the entire spectrum range as itcompares the sample f more in detail in our specific description ofapparatus constituting a preferred embodiment of our invention and byreference to the accompanying drawings in which we have illustrated ourinvention' as embodied, for example, in'an automatically recordingcolorimeter..

In the drawings: v

Fig. 1 is a diagrammatic plan view, with certain parts broken away,illustrating the complete apparatus and showing the variou electricalcircuits; v

Fig. 2 is an enlarged detail illustrating one arrangement of amplifiercircuit useful in connection with the apparatus of Fig. 1; Fig. 3 is afragmentary vertical section, to

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large lscale, substantially on the line 3--3 of Fig. 1; u

Fig. 4 is a fra entary vertlcal section n the hne 4--4 of ig. 3;

Fig.^5 is a fragmentary elevation showing the shutter device forcontrolling the intensity of illumination from the standard source;

Fig. 5 is an edge elevation of the device shown in Fig. 5;

Fig. 6 is a section substantially on the line 6-6 of Fig. 1, to largerscale, showing details of a current rectifying device;

Fig. 7 is a section, to larger scale, of th light-flashing disk; and vFig. 8 is a diagram illustrating the type of record which is produced bythe apparatus here disclosed.

Referring to the drawings, the numeral l designates a suitable basewhich is here shown as carrying the various elements of the apparatus,together with the wiring forming the electrical circuits. It is to beunderstood that the arrangement shown in Fig. 1 is merely illustrativeand that various portions of the apparatus ma be mounted upon separatesupports an may, and preferably will in some instances, be widely searated.

pon the base 1 we mount a light source 2, conveniently an incandescentlamp, preferably having a fiat filament 3 which is disposed in the planeindicated in Fig. 1. IvAt one side of the lamp 2 we provide a support 4adapted to hold a sample to be tested or a standard of comparison. Wehave here illustratedthis support 4 as holding the standard ofcomparison. This support is preferably provided with a shield 5 havingan aperture through which the substantially dat surface 6 of thestandard 7 is exposed to the light of the lamp 2. We nd that for colorcomparisons a block of magnesium carbonate constitutes a very desirablestandard as such a block reflects a very pure white light.

At the opposite side of the lam '2 and conveniently at the same distanceom the lamp as the support 4 we mount a second support 4', also providedwith a shield 5` having a slit or a erture through which the flatsurface 8 of t e test sample 9 is exposed to the light from the lamp.

Between the lamp and the support 4 -we preferably arrange a set ofcondensing lenses 10, and we also arrange a similar set of condensinglenses 11 between the lamp and the support 4. In order to avoid-overheating the sample and the standard we preferably interpose at asuitable point between the lamp and each of the supports 4 and 4 coolincells 12 and 13, respectively.

e also interpose between the lamp and the supports 4 and 4 a air ofshutter or diaphragm devices 14 an 15, respectively,

adapted to' cut o' more or less of the light from the lam and thus todetermine the amount of lig t' reiected from the exposed surflaces ofthe standard and sample, respective y. l

Referring to Figs. 5 and 5", we have shown one form of shutter device 14in detail, it being understood that the shutter device 15 may be ofsimilar character. The shutter de vice 14 comprises a pair of plates 14and 14", which may conveniently take the form of disks. Each of thelates 14 and 14b is preferably provided wit alternating opaque andtransparent quadrants. These quadrants may conveniently be formed bypunching outthe plates so as to leave openin s such as 16 alternatingwith quadrants which are not punched out. By turning one of the platesrelatively to the other it is evident that the open quadrants may bebrought into registry, thus permitting a maximum amount of light to passthrough the shutter device, while, on the other hand, by adjusting theplates properly the registering portions of the open quadrants may bedimmished in area until, if desired, the, opening is completely closed.

As-shown 1n Fig. 5 the edge of the disk or plate 14a is provided withgear teeth 17 which mesh with a worm or pinion 18 on a shaft 19 which is,mounted in suitable bearings carried bythe support 1. The means forrotating this shaft is hereinafter more fully described.

The movable plate or disk of the shutter device 15 is preferablyprovided with an arm 'or other means contacting with a cam 20 mountedupon a shaft 21 which is rotated by means hereinafter more fullydescribed. By suitably shaping the cam 20 the shutter device 15 may beadjusted in one direction 0r the other and at such varying speed as maybe desired.

A shaft 22 is mounted to turn in suitable bearings carried by the base 1and this shaft is arranged substantially parallel to the optical axes ofthe condensing lenses 10 and 11, that is to say, the shaft 22 issubstantially erpendicular to the planes of the exposed aces'6 and 8 ofthe standard and the test sample, respectively. The shaft 22 ispreferably provided with a gear 23 meshing with a pinion upon the shaftof an electric motor 24 which is connected by suitable lead wires to themains 25 and 26.

The shaft 22 carries a dashing device 27 which comprises a disk,preferably of glass, having alternating transparent quadrants 28 andrefiecting quadrants 29. The reflecting surfaces of the quadrant 29 areturned toward the light reflected from the test sam le 9 and the p aneof the disk is so locate makes substantially equal angles with beams oflight B1 and B2 reiiected from the surfaces 6 and 8 of the standard 7and sample 9, respectively. For properly directing these that itl EXMNERbeams of light we preferably interpose lenses 30 and 31 in such beams.As indicated in Fig. 1, the beam B1 of light reflected from the standard7 passes through the Alens 30 and through the .transparent sectors 28 ofthe flasher disk 27 and through a narrow slit 33 in a shield 32 disposedadjacent to one upon the rod 37 face of the disk. 0n the other hand thebeam 132 reflected from the test sample 9 impnges upon the reflectingsectors 29 of the disk 27 and is reflected from these reflectingsurfaces so that it passes along the same path L as the beam B1 andthrough the slit 33. The revolution of the shaft 22 with its disk 27thus causes light reflected from the standard 7 and from the testsample9 to pass in alternate flashes through the slit 37 along the path L.These alternating flashes of light next pass through a lens 35 and intoa prism 34 which disperses the light to form an extended spectrum. Wepreferably interpose a lens 36 in the path of the light emerging fromthe prism 34 and the light from this lens 36 forms an extended spectrumband S witIl the violet end at V and the red end at In suitable bearingswe mount a sliding bar 37. This bar 37 carries a shield 37 1 providedwith an aperture or slit 38. Preferably We secure one end of a quartzrod or tube 39 to the shield 37* with the end of the rod or tube exposedat the aperture 38. This rod or tube 39 is mounted in a swivelingsupport 39 so that it may swing in accordance with the movement of thesliding bar 37. The opposite end of this rod or tube 39 is directedtoward the window of a photoelectric cell 40. While we prefer to use aquartz rod or bar for directing the light from the aperture into thewindow of the photoelectric cell we may employ a series of mirrors .forthis purpose or We may, if desired, mount the cell so that the c'ellwill travel with the aperture 38. Moreover, while a photoelectric cellis a desirable instrument forour purpose, we contemplate that otherdevices having generali similar character istics may be su stitutetherefor.

-We preferably enclose the photoelectric cell 40 or e uivalent device ina suitable shielding enc osure 41 which may consist of a frame coveredwith wire mesh or other arrangement adapted to protect the cell fromfortuitous electrical disturbances.

Since the current in such a cell is extremely small, being, for example,of the order of 10'1" amp., such current is of little value either forobservational purposes or for actuating any mechanical device, andaccordingly we provide means for amplifying th1s current. As shown inFig. 2 we have provided three stages A1, A, A11 of amplification,employing thermionic tu s or equivalent deviceswhich may be ofwell-known character,

a5 connected in suitable circuits which may be varied according toconditions, such circuits forming no essential part of the presentinvention, although usually such circuits will include condensers C1, C,Cs and C, or means equivalent for the purpose.

The amplified current from the last stage of amplification is conductedthrough wires 43 and 44 to a rectifying device 45 mounted upon theshaft22 so that it operates in synchronism with the flashing disk 27.

This rectifier preferably comprises a support carryin insulatedconductmo' segments 46 and 47, w ich are engaged by brushes 48, 49, 50and 51. The brushes 48 and 50 are connected to the wires 43 and 44,respectively, while the brushes 49 and 51 are connected by Wires 52 and53 to the terminals of a direct current galvanometer relay G. Inaccordance with the movement of the alvanometer contact a circuit iscompleted t rough wires 54 and 55 or through Wires 54 and 57, resectively. The wire 54 is connected wit a suitable source of current, forexample the battery B3. The wire 57 is connected by a wire 571 to oneterminal of the magnet 58 of a relay device R2. The other terminal ofthe magnet 58 is connected by a wire 59 to the battery B11. The wire 591s also connected to one terminal of the 'magnet 69 of a second relayR3. The other terminal of the magnet 69 is connected by the wire 67 tothe wire 55.

One terminal of the magnet 56 of a third relay R1 is connected to theWire 59 and its other terminal -is connected by Wire 60 to one contactof a key switch 61. The other contact of the key switch is connected bythe wires 62 and 63 to a circuit closer 64 comprising an insulating diskhaving a metal segment at one part in its periphery and which is mountedupon aY shaft 65 supported in bearings upon the base 1. A wire 66extends from this circuit closer to the' wire 55. Wires 63" and 63cextend from the same circuit closer 64 on shaft 65 to the Wires 54 and57, respectively. n electric motor M1 is mounted on the base 1 and theterminals of this motor are connected by wires 70' and 71 to the relaydevice R1. This relay device comprises a fixed terminal 72 and a movablecontact member 73, the movable contact being u'nder the control of themagnet 56. The relay R1 controls the -flow of current from supply wires7 2" and 7 31 to the motor M1.

A reversible electric motor M2 is mounted upon the base 1 and the fieldofv this motor is connected by a wire 74 to the-movable contact 75 ofthe relay R1. One fixed contact 79 of this relay is connected to thesulply wire 25, which is also connected to one xed contact of the relayB. The other eld terminal of the motor M is-connected by wire 77 to themovable contact 78 of the rela R. One terminal of the armature of motor1 is connected by a wire 76 to the supply main 13g ZDUZUL 26, while theother amature terminal is connected b a wire 76 to circuit breakers 103and 104 ereafter described. A wire 76h connects the other fixed contact76c of the relay4 R1 to the circuit breaker 104.

A wire 76e connects the fixed terminal 76r of relay IR2 to the circuitbreaker 103.

The shaft 65, which carries the circuit closer 64, also carries a cam 81which engages a cam follower roll 82 mounted upon a bracket 83 carriedby the slide bar 37. Springs 84 hold the cam follower roll 82 in contactwith the cam 81. Thus, as the shaft is rotated the bar 37 is caused toslide in its guideways moving the aperture 38longitud1- nally of thespectrum band S and thus exposin the photoelectric cell 40 progressivelyto lig t of the varying Wave length.

The shaft 65 also carries a drum 85 which may support a wax cylinder, asheet of paper or other surface adapted to receive a recor 'The shaft 65is provided with a gear 86 meshing with a gear upon the shaft 87, whichin turn carries a gear 88 meshing with a pinion 89 on the shaft of the imotor M1.

The shaft also carries suitable drive means 90 for actuating a shaft 91which in turn, by means of suitable gearing 92, turns the shaft 21carrying the cam 20 which adjusts the shutter 15.

The shaft 19 which carries the means for adjusting shutter 14 isprovided with a ear 95 meshing with a pinion 96 on the sha t of themotor M2 and thus in accordance with the direction in which the motor M2turns the shaft 19 is turned in one direction or another, thus openingor closing the shutter 14.

The shaft 19 is provided with a screwthreaded portion 97 engaging a nutmember' 98 forming part of a reciprocating carriage 981 which supports alever 99 overlying t e surface of the drum` 85 and carryin stylus 100adapted to cooperate-with the rum in producing a record. Thereciprocating carriage is provided with a rearwardly extending portlonhaving a slot 102 which receives a metallic guide rod 101 carried ininsulating supports on the base member 1. The rod 101 preferablysupports the circuit breakers 103 and 104', respectivel disposedadjacent to opposite ends of the rum. These circuit breaking devices areconnected in circuit with the motor M2 as above described. Each circuitbreaking device comprises normally engagin contacts, one of which ismovable and is 'sposed in the path of a rod 105 mounted upon thecarriage, so that as the carriage approaches one end or the other of thedrum, rod 105 will en age the corresponding circuit breaking evice, andthus break the circuit through the motor M2,so

i that overtravel of the carriage will be automatically prevented.

The carriage also supports a contact device CROSS REFERENCE 106 which isin conducting relation to rod 101 and which is disposed between a fixedcontact 107 and an adjustable contact 108 mounted upon metallic slideblock 109 carried by a bar 110 mounted in insulating supports on thebase 1. The rod 101 is connected by a wire 106l with the wire 62 and thebar 110 carrying contacts 107 and 108 is connected by the wires 63 and63b to the circuit of relay R1 so that whenever the contact 106 engagesone of the contacts 107 or 108 the magnet 56 is energized and thecircuit o f motor M1 is broken. Thus, as the carnage moves in onedirection or the other, bringing the member 106 into engagement with oneof the contacts 107 or 108, the drum motor M1 is stopped while the motorM2 continues to operate in the endeavor to set shutter 14 so as tobalance the light from the sample and standard. During this movement thestylus 100 moves along an element of the drum cylinder, while the slideblock 109is pushed along by the contact 106. The momentum of the movingparts is such that when balance has been attained and the circuitthrough motor M2 has been broken the shutter is moved just a littlebeyond the bal- -ture V38 at a new point in the spectrum and ltheoperation of balancing is repeated.

In the operation of the device the standard 7, which, as above stated,is conveniently a block of magnesium carbonate having a smooth planeface 6, is mounted upon the support 4, and the sample to be tested ismounted upon the support 4 with its surface 8 exposed at the slit 1n theshield 51. The lamp is now lighted and light from the lamp gasses inopposite directions through the conensing elements 10 and 11 andilluminates the standard 7 and the sample 9. The light reiected from thesurfaces 6 und 8 passes through the lenses 30 and 31 and by the rotationof the disk 27 is despatched in alternating flashes along the line Lthrough the lens 35 to the prism 34. The prism disperses this lightwhich passes through the lens 36 and forms the s ectrum band b. It beingassumed that the sllde 37 is in the position indicated in Fig. 1 wherethe aperture 38 is exposed at the red end of the spectrum and that theshutters 14 and 15 are so adjusted that a greater amount of red light isreflected from the standard 7 than from the sample 9, the energyrepresented by the flashes from the standard will be eater at the redend of the spectrum than t e energy from the dashes received from thesample. Thus the photoelectric cell 40 will be subject to alternatingvariations in energy so that a pulsating current will be set up in thiscell. This current is amplified by passage through the amplifyingcircuit and after amplification passes to the rectifier 45 where it isrectified and thence passes to the galvanometer G. In accordance withthe direction of the current in any instant the current flows eitherthrough the leads 54 and 55 or through the leads 54 and 57. Assumingthat the current fiows through the leads 54 and 57, the magnet of therelay R2 will be energized, drawing the contact 75 over against theContact 79 and thus completing a circuit through the motor M2 in adirection such as to turn the sliaft'19 so as gradually to close theshutter 14. This operation continues until the shutter has cut ofi lightfrom the standard 7 to such an extent that the red rays from thesandal-d are no stronger than those from the test sample 9. When thisresult has been reached the flashes o`f light received at thephotoelectric cell will be of substantially equal intensity, whereuponthe current in such cell becomes uniform and the amplifying circuit isineffective. The galvanometer G thus moves to zero position, the magnet58 is de-energized, and the circuit through the motor M2 is broken, thusstopping the shaft 19 and the shutter 14.

`which cause rela 15 may be adjusted by the cam 20-so as to vary thelight received from the test sample at a predeterminated rate (inaccordance with the position of the aperture 38 with respect to thespectrum) ratio of reflection 'of the reiecting surfaces of the disk 27at different parts of the spectrum.

If at any time the carriage should reach one end or the other of thedrum, the circuit breaking device 105 will break the circuit at 103 or104, respectively, through the motor M2 so as to prevent the stylus fromruiming off the end of the drum. Further, after each complete revolutionof the shaft 65 the cir cuit closer 64 automatically closes circuits R1to open circuit through motor M1 and w ich canse whichever of the relaysR2 and R3 is then in operation to open the circuit through motor,M2,thus causing both motors to stop. 4

In Fig. 8 we have appearance of a record such illustrated the general asproduced by our apparatus, showing the results of testing As thebeginnin' of the above sequence of i operations started, the movablecontact 73 of relay R1 was in en agement with contact 72, thuscompleting t e circuit through drinn driving motor M1.

magnet 56 be energized at the start of the operation, thus holding thecircuit open, it may be deenergized to close the motor circuit byactuation of key 61. As the rotation of the shaft 19 causes thereciprocating carriage 98 to move longitudinally of the drum, the stylus100 immediately begins to make a`rec ord upon the drum and so long asthe carriage continues to move the stylus continues to form such recordlines on the drum.

In adjusting the shutter 14 to obtain equal ener from the standard andfrom the test samp e, the momentum of the parts produces overtravelwhich results in a read] ustment and a restarting of the motor M1, thusactuating the cam 81 and moving the aperture 38 to a new point in the sectrum. .At this point the energy may again e different as received fromthe standard and from the test sample. Thus, immediatelythephotoelectric cell may .become operative either to re-energize therelay R2 or in accordance with a different indi'- cation of thegalvanometer to energize the relay R. In the first case the motor Mz maybe set into operation in the same direction as reviously, while in thelatter case the motor 12 turns in the reverse direction, thus causingthe carriage ,with the stylus 100 to move oppositely to its originaldirection. At the same time the shutter 14 is moved in the appropriatedirection either to decrease or increase the amount of light reflectedfrom the standard.

During If forI any reason the samples of yellow and blue tone,respectively.

While the above arrangement is desirable and useful we contemplate thatvarious changes in the elements employed, as well to compensate for thevary f as in their arrangement, may be made without departing from thespirit of the invention. Thus in place of electric motors we contemplatethat fluid pressure motors may be employed under some circumstances andpossibly to some advantage in that such motors would not have anytendency to interfere with the sensitive operation of the photoelectriccell. We also contemplate that the shutters 14 and 15 may be dis osedinthe reflected beams of light B1 an Bz instead of between the sourceofillumination and the andard and test sample and that either or bothshutters may be actuated for balancing the light. We also contemplatethat in place of the prism 34 other dispersing means, for example agrating, might be employed, and as above described we also contemplatethe substitution of equivalent means for the photoelectric cell 40 andfor the amplifying ciry cuit herein described.

certain aspects of the invention are contained the above operations theshutter said in the Hardy application Serial No. 274,448,

-filed May 2, 1928, and entitled Method of and apparatus for comparingand recording radiant energy, while claims of more limited scope arecontained in the Hardy and Cunningham vapplication Seria No. 274,729,filed .May 3, 1928, and entitle Method of and apparatus for comparingradiant energg. l n eclaimz' 1. That method of determining the, colorlcharacteristics of a test sample which comprises as steps deliveringbeams of light from sample and .from a. standard of comparison,dispersing said beams to form extended spectra,y exposing a sensitivelyresponsive device in which an electric current varies in accordance withthe luminous energy received by said device alternately to acorresponding part of each spectrum, ampliying the current in saiddevice, rectifying said amplified current by means synchronized with thealternations of exposure of the device to said spectra, and employingthe rectified current to cause such exposures of said sensitive devicesuccessively to occur at different portions of the spectra.

2. That method of comparing radiant energy from different sources whichcomprises as steps alternately delivering flashes of energy from eachsourceto a sensitively responsive device inwhich an electrical currentvaries in accordance with the radiant energy received by said device,amplifying the current from said device, rectifying the amplifiedcurrent, and employing said rectied current in varying the energyreceived from one of said sources until the current in said sensitivedevice becomes substantially constant.

3. That method of determining the color characteristics of a test samplewhich comprises as steps illuminating the test sample and a standard ofcomparison to provide two sources of reflected light, alternatelydeliverf ing reflected light from said respective sources to asensitively responsive device in which an electrical current varies inaccordy ance with the amount of luminous energy delivcred to saiddevice, amplifying said varying current, rectifying the amplifiedcurrent providing means for changing the amount of light delivered fromone at least of said means, and employing said rectified current forcausing said light changing means to act until the current in saidsensitive device becomes substantially constant.

4. That method of determining the color characteristics of a test samplewhich comprises as steps delivering beams of light from said sample andfrom a standard of comparison, dispersing said beams to form extendedspectra, exposing a sensitively responsive device in which an electriccurrent iluctuates in accordance with variations in the luminousenergyreceived by said device alternately to a corresponding part of eachspectrum, and employing` the current from said sensitively responsivedevice for controlling the variation of energy delivered from thestandard until the current in said device substantially ceases tofluctuate.

5. That method of determining the color characteristics of lightreflected from a test sample which comprises illuminating said sampleand a standard of comparison, delivering reected beams alternately andin rapid succession from' the sample and standard respectively `todispersing means whereby al- CROSS 'REFEREMCE ternatel to form anextended spectrum of each re ected beam, exposing a photoelectric cellto a corresponding portion of each of the alternating spectra, employingthe current in said cell in automatically varying the intensity of lightfrom the standard.

6. That method of determining the color characteristics of a test samile which coniprises as steps delivering eains of light from said sampleand from a standard of comparison, dispersing said beams to formextended spectra, ex osing a sensitively responsive device in which anelectric current varies in accordance with the luminous energy receivedby said device alternately to a corresponding part of each spectrum,amplifying the current in said device, rectifying said amplified currentby means synchronized with the alternations of exposure of the device tosaid spectra, and ein lo ing the rec-- tified current for varying t euminous energy delivered from the standard and for recording suchvariation in energy.

7. That method of determining the color characteristics of a test samplewhich com` prises as steps illuminating the test sample and a standardto provide sources of light, alternately delivering light from saidsources to a sensitively responsive device in which an electricalcurrent varies in accordance with the amount of luminous ener deliveredto said device, amplifying sai varying current, rectifying the amplifiedcurrent, varying the amount of light delivered from one of said sources,provi ing means for recording the variation in light, and employing saidrectified current in determining the actuation of said recording means.

8. That method of comparin radiant energy from diferent sources whichcomprises as steps alternately delivering flashes of energy from eachsource to a sensitively responsive device in which an electrical currentvaries in accordance with the radiant energy received by said device,ampli 'ng the current through said device, recti g the ainpliiiedcurrent, providing means for varying the energy received fromone of saidmeans and for recording said variation, and employing said rectifiedcurrent to determine actuation of said energy varying and recordingmeans.

9. That method of determining the color characteristics of a test samplewhich comprises as steps deli'ering beams of light from said sample andfrom a standard of comparison, dispersing said beams to form extendedspectra, exposing a sensitively responsive device in which an electriccurrent varies in accordance with'the luminous energy received by saiddevice alternately to a corresponding part of said spectrum, amplifyingthe current in said device, rectifying said amplified current by meanssynchronized with the alternation of exposure of the device to saidspec- EXAii/HNER posing sai 25 tra, and employing the rectiied currentfor controlling the actuation of means for varying the luminous enerdelivered from the standard, to cause suc exposure of the sensitivedevice successively to occur at different portions of the spectrum, andfor r'ccording the energy delivered from said source at each such partof exposure.

10. Apparatus for comparing radiant energy from different sourcescomprising a device in which the electrical current varies in accordancewith radiant energy received by said device, means for alternatelydelivering flashes of energy from each of said sources to said device,means for amplifying the current from said device, means for rectifyingthe amplified current, and means responsive to said rectified currentfor varying the energy received from one of said sources until thecurrent in said sensitive device becomes substantially constant.

11. Apparatus of the class described comprising a hotoelectric cell,means for exd) cell alternately to light of a selected wave lengthreceived from a test sample and a standard of comparisonl'respectively,and means responsive to fluctuation of the current in said cell forvarying the luminous energy delivered from the standard of comparison.

12. Apparatus for determming the color characteristics of lightreiiected from a. test sample comprising a source of illumination, meansfor supporting the sample and a standard of comparison, means fordirecting light from the source of illumination onto the standard andthe test sample respectively, means for dispersing light to form aspectrum, rotary means for alternately delivering flashes of reflectedlight from the test sample and standard re tively to the dispersingmeans, a photoe ectric cell exposed to the spectra produced by thedispersing means, means for amplifying the current from said cell, meanssynchronized with the rotary flash reducing means for rectifymg theamplified) current, and means controlled by said rectified current foradjusting the 1ntensity of the ashes of light from the standard untilthe current in the photoelectric cell becomes substantially constant.

13. Colorimeter ap aratus compnslng means for alternately eliveringlight of a given wave length from a test sample and a standardrespectively to a hotoelectric cell, a shutter for determining t e lightdelivered by said standard, a motor for actuating said shutter, andmeans responsive to the current in said cell for determining theactuation of said motor.

14. Apparatus of the class described comprising means for supporting atest sample and a standard of comparison, rotary means for producingalternating flashes of li ht from said sample and standard, a photoe ec-1, h sa' tric cell responsive to said alternating iashes, means foramplifying the current -in said cell, means synchronized with the rotaryflash producing means for recti g said current, means responsive to sairectified current for determinin the amount of li ht delivered by thestan ard, and 'means or varying the light delivered from the sample.

15. Apparatus for comparing radiant energy froml different sourcescomprising a sensitive device in which an electrical current varies inaccordance with the radiant energy received by said device, said devicereceiving energy from the several sources successively, means foramplifyin said current and for rectifying the ampli ed current, andmeans responsive to said rectified current for adjusting the energydelivered from one of said sources and for recording such adjustment.

16. A colorimeter comprising means for dispersin light from a testsample to form an exten ed spectrum, a substantially stationaryphotoelectric cell, automaticall operating means moving lengthwise o thespectrum for progressively exposing the photoelectric cell to lightwaves of different lengths, and means responsive to fluctuations incurrent in the cell for varying the intensity of light from the sample.

17. A colorimeter comprising means for dispersing light from a testsample to form an extended spectrum, a photoelectric cell, and a quartzrod having one end always directed toward the cell, and having itsopposite end movable longitudinally of the spectrum, and means formoving said latter end whereby progressivelyA to transmit light frplmvarious portions of the spectrum to the ce 18. A colorimeter apparatuscomprising means for delivering light of a predeterl `refiected fromsaid standard white surface, a

reversible motor for actuating said shutter, a stylus also actuated bysaid motor, a rotary drum cooperating with said stylus for making arecord, a motor forturning the drum, and means responsive to the currentin the photoelectric cell for determining the direction of rotation ofthe shutter actuating motor.l l

19. A- colorimeter apparatus comprising means for directing light inalternate flashes from a test sample and a standard of comparisonrespectively onto a photoelectric cell, a shutter for adjusting theamount of light delivered from said standard, a reversible motor foractuating the shutter, a stylus also actuated by said motor, a movablerecord surface cooperating with the st lus, means for moving said recordsurface an for nate iiashes of light to said cell from a standchronouslyvarying the wave length of ii? ,ard of comparison and a test samplerespectively,

a shutter for varying the amount of light delivered by the standard, astylus, reversible motor means for determining the movement of thestylus and shutter, a rotary drum cooperating with the stylus, means forturning the drum, a cam turning with the drum, means actuated by the camfor. determining the wave length of light to which the photoelectriccell is at any time exposed, and means responsive to the current in saidcell for controlling the direction of 4movement of thc shutter actuatingmotive means.

21. A coloi'imeter apparatus comprising a hotoelectric cell, means fordeliverin light in alternating fiashes from a test samp e and a standardof comparison respectively .tothe cell, a shutter for varying the lightdelivered by the standard, means for reversibly moving the shutter andfor moving the stylus 1n opposite directions in synchronism with theshutter, aI rotary drum, motor means for turning the drum, and meansmoving in synchronism with the stylus for determining the actuation ofthe drum driving motor.

22. Apparatus for determining the color characteristics of a test samplecomprising means for supporting a samp e and a standard of comparison,means or illuminating the sample and standard, means for dispersinglight to form a spectrum, a rotary disk having alternating sectors whichare transparent and which are reiecting surfaces, means for deliveringlight from the standard and test sample in paths making substantiallyequal angles with opposite faces of the disk, means for rotating saiddisk whereby light from the standard and from the test sample istransmitted in alternating flashes to the dispersing device, aphotoelectrie cell exposed to the spectra produced by the-dispersingdevice, means for amplifying the current from said cell, restifyingmeans synchronzed with the rotating disk for rectifying the amplifiedcurrent, a galvanometer relay responsive to said rectified current, ashutter for determining the amount of light delivered from the standard,a reversible electric motor for moving said shutter, relay devices fordetermining the direction of movement of said motor, means connectingsaid relay devices to the galvanoineter relay whereby the latterselectively determines actuation of said relays, an indicator devicemoving synchronously with the shutter actuating means, a rotaryrecording drum cooperating with said indicator device, means for turningthe drum,

CROSS Ratas-:et

means moving with the indicator device for determining operation of thedrum moving means, means turning in synchronization with the druin fordetermining that portion of the spectrum to which the photoelectric cellshall be exposed, and means moving in synchronization with the drum forvarying the amount of light delivered to the test sample to compensatefor the variable reiiection factor of the reflecting surface of therotating disk at different wave lengths.

23. In the art of comparing radiant energy from dierent sources bynieans of a sensitive device, the method of alternately deliveringflashes of energy from each source to the sensitively responsive devicein which an electrical current varies in accordance with the radiantenergy received by said device, amplifying the current from said device,and employing said amplified current in varying the energy received fromone of said sources until the current in said sensitive device becomessubstantially constant.

24. In the art of determining the color characteristics of a test sampleby means of a sensitively responsive device and a standard ofcomparison, the method which comprises illuminating the test sample andthe standard of comparison to provide two sources of reflected light,alternately deliver- LN-ilumina ing reiiectcd light from said respective9 rent for causing said light changing means to act until the current insaid sensitive device becomes substantiall constant.

25. In the art o determining the color characteristics of -a test samplewhich employs a sensitively responsive device and a standard ofcomparison, the method of delivering beams of light from said sample andfrom the standard of com arison, dispersing' said beams to form extented spectra, exposing the sensitively responsive device in which anelectric current varies in accordance with the luminous energy receivedby said device alternately to a corresponding part of said spectrum,amplifying the current in said device, and employing the amplifiedcurrent for responding respectively to the two sources, comparing theintensity of illumination at corresponding parts of said spectra, andcausing differences in intensity at the point of comparisonautomatically to vary the relative intensity of the sources.

27. That method of color comparison which comprises as steps comparingthe intensities of li ht of selected corresponding wave lengths rom twosources, and causing difference in intensities at the selected point ofcomparison automatically to vary the relative intensities'of the sourcesuntil the intensities at the selected wave lengths are equal.

28. In the art of comparing light intensities from two sources whichemploy a rever- 'sible motor and a photoelectric cell, the

method of delivering alternate flashes of light from the two sources tothe photoelectric cell, and determining the direction of ro- -tation ofa reversible motor in response to the phase of the cell current.

29. Apparatus for comparing radiant energy from different sourcescomprising a device in which the electrical current varies in accordancewith radiant energy received by said device, means for alternatelydelivering liashes of energy from each of sa1d sources to said device,means-for amplifying the current from sa1d device, and means responsiveto said amplified current for varying the energy received from one ofsaid sources until the current in said sensitive device becomessubstantially constant.

30. Apparatus of the class described comprising a hoto-electric cell,means for exposing sai cell alternately to light received from twosources, respectively, means for amplifying the current from saidphotoelectric cell, and means controlled by said amplified current forvarying the amount of light delivered from at least one of said sources.v D

31. A paratus for comparing radiant energy iL-)rom different sourcescomprising a sensitive device in which an electrical current varies inaccordance with the radiant energ received by said device,means forampli 'ng said current and means responsive to said amplified currentfor adjusting the energy delivered from one of said sources and forrecording such adjustment. 32. Apparatus of the class describedcoinprising means for exposing a light sensitive cell alternately tolight from two sources, and means res onsive to iuctuation in current insaid cell or varying the intensity of light from one of said sources.

33. Apparatus of the class described coinprising means for exposing a.light sensitive cell alternately to light of corresponding wave lengthfrom two sources, and means responsive to fluctuation. in current in thecell for equalizing the intensity of light received by the cell from therespective sources.

by such light sensitive element for automatically equalizing theintensity of ligli-t from the two sources.

36. Apparatus of the class described comprising means for comparing therelative intensity of light from two sources, a part which moves in onedirection or the other in accordance with the preponderance in intensityof the light from one source or the other, respectively, and meanscontrolled by .said moving part for automatically varying the relativeintensity of the light from the two sources.

37. Apparatus of the class described comprising means for comparing therelative intensity of light from two sources, a part Which'moves in onedirection or the other in accordance with the preponderance in intensityof the li ht from one source or the other, respective y, and meanscontrolled by said moving part for automatically balancing the intensityof lift from the two sources. i y

38. Apparatus of the class described comprising means for comparing therelative intensity of light from two sources, a part which moves in onedirection or the other in accordance with the preponderance in intensityof the li ht from one source or the other, respective y, and meanscontrolled by said moving part for automatically recording the relativeintensity of light from the two sources.

39. Apparatus of the class described comprising means for comparing therelative intensity of light from two sources, a part which moves in' onedirection or the other in accordance with the preponderance in intensityof the li ht from one source or the other, respective y, and meanscontrolled by said moving part for automatically balancing the intensityof light from the two sources and for recording the point of balance.

40. Photometer apparatus for comparing light intensity from two sources,said photometer comprising a part which is illuminated by light from thetwo sources, and automatic means, operatively responsive to the relativeintensity of illuc'mination of sa1d part by the two sources, forequalizing the intensity of illumination of such part. by the respectivesources.

4l. Apparatus for determining the color characteristics of a test'samplecomprising erated by the motor for var ing the energy means fordelivering flashes of light alterfrom one of said s ources, an meansi'or connately from two sources, the light from one trolling thedirection of motion of the motor source encountering a reflectingsurface, a in accordance with the phase of the current.

5 shutter for varying the iitensity of the light 46. Apparatus forcomparing light intensi- \\'hich is reflected, and rotary cam means forties from two sources comprising a photoelecadjusting the shutter tocompensate for the tric cell, means for exposing said cell altervariablereflecting factor ofthe reflecting surn ately to light 'from said twosources res ecface when reflecting light of different wave tlvely, areversible motor, means operate' by lengths. the. motor for varying theamount of light 42. Apparatus for determining the color delivered tosaid cell from one of said sources, characteristics of a test sample,comprising and means for controlling the direction of m0- means forsupporting a Sam 1e and a standtlOli 0f the mOOr 1n aCCOIdaIlCe With thephase ard of comparison, means or illuminating 0f the C611 CUTIBU- tliesample and standard, arotary disk having 47. Apparatus comprising ahotoelectric 80 alternating sectors which are transparent Cell, .meansOI alternately dellveringl light and which are reflecting surfacesiespective- Wlllm a Wave length range less than t e visi- 1y, means fordeliveriner light from the standble SPBCIllm flOm a test Sample and astandard and sample in pat s making substantialard res ectively to saidcell, a reversible moly equal angles with opposite faces of the disk,OI, fm, means fOr Controlllng the direction 85 means for rotating thedisk whereby light 0f mO'ClOIl Of the mOtOI 1n aCCOIdanCe with the ifrom the standard and from the sample is Phase 0f the Cellcurrent.

transmitted in alternating flashes, and means 48- A GOlpHmetel'apparatus Comprising a for varying the amount 0f light deliveredphotoelectric cell, means for delivering light from the test Sam le tocompensate for the 9i a predetermined Wave length in alternato variablereflection actor of the reflecting surmg aSllP-S IOIB a test Sample anda Standard face of the rotating disk at different wave FQSPGCUVQIY t0Sad C5511 means for determi?- lengths, ing the amount of light reflectedfrom said 43. Apparatus for determining the color standard, a reversibleelectric motor for accharacteristics of a test sample comprising ultmgsaid latter means, and means o erat- 95 means for supporting a sam leand a standmg SYDChIOIlOUSlYv With the -flash pro ucing and ofcomparison, means 0r illuminating means for determining the direction ofrotathe sample and standard, means for disperstion of the motor inresponse to the phase of ing light to form a spectrum, a rotary disk theC811 Currenta5 having alternating sectors which are trans- Signed by 11Sat Cambridge, Massachusetts 100 parent and which are reflectingsurfaces, rethis 18th da 0f Ma 1927.

spcctivel means for delivering light from ARTH C- ARDY- the stan ard andtest sample in paths mak- FREDERICK W. CUNNINGHAM. ing substantiallyequal angles with plane of the disk, means for rotating the disk whereby105 to transmit light from the standard and sample in alternatingflashes to the dispersing device, a shutter for varying the amount oflight delivered to the test sample, and cam means for actuating saidshutter'whereby to 110 compensate for the variable reflection factor ofthe reflecting surface of the rotating disk at dilferent parts of thespectrum. A

44. Apparatus of the class described coinprising a pliotoelectric cell,means for alter- 115 nately flashing Vlight from two sources upon thecell, a reversible motor, means operated 'by the motor for varying theintensity of one of said light sources, and means operatingsynchronously with the flash producing means 1z0 for determining thedirection of rotation of the reversible motor in response to the phaseof the cell current.

45. Apparatus for comparing radiant energy from different sourcescomprising a de- 125 vice iii which an electrical current varies inaccordance with radiant energy received by said device, means foralternately delivering flashes of energy from each of said sources iesto said device, a reversible motor, means op-

